1. Field of the Invention
The present invention relates to a method utilized in a wireless communication system, and more particularly, to a method for handling a multimedia broadcast multicast service (MBMS) minimization of driver test (MDT) in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard is developed by the 3GPP as a successor of a universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provide high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques such as carrier aggregation (CA), coordinated multipoint (CoMP) transmission/reception, uplink (UL) multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Multimedia broadcast multicast service (MBMS) service or evolved MBMS (E-MBMS) service has been introduced in the UMTS, the LTE system and the LTE-A system, for broadcasting multimedia contents such as TV programs, films, music, etc. Compared with the traditional unicast, the MBMS service (hereafter referred to both the MBMS service and/or the E-MBMS service) is provided in downlink only, and is broadcasted from the network to multiple (e.g., a specific group of) UEs via a point-to-multipoint transmission. Characteristic of the MBMS service enables the network to provide the MBMS service to unlimited number of UEs with a constant network load. In addition, a UE in the UMTS, the LTE system and/or the LTE-A system may receive the MBMS service inherently, and no additional hardware component is needed to be installed for the MBMS service. Thus, the MBMS service is attractive, considering both hardware cost and resource efficiency.
Multicast-broadcast single frequency network (MBSFN) is a communication channel defined for the MBMS service. In MBSFN transmission, signals from several antennas of potentially different base stations are combined in the UE. This combination makes MBSFN transmission different from unicast transmission, and makes the performance of MBSFN transmission difficult to be verified than unicast transmission. MBSFN transmission is unacknowledged. There is no feedback to the radio access network (RAN) which broadcasts the MBMS transmission, such as hybrid automatic repeat request (HARQ) or radio link control (RLC) acknowledgements, meaning that the RAN does not know whether the MBSFN transmissions are successfully received or not. Hence, it is difficult for an operator to understand the quality of MBMS services being delivered. Thus, the only way to verify and optimize MBSFN radio transmission is to do manual drive test.
Unfortunately, using manual drive tests for network optimization purposes is costly, and this contributes in environmental emission of CO2 and more importantly, comes with a limitation in measuring places along a drive route which is generally not typical to where customers consume MBMS services.
Minimization of drive test (MDT) functionalities, including logged MDT and immediate MDT, are performed or logged by UEs to collect information (or called measurement logs) in the idle mode or connected mode, and report the information to the network, to reduce network maintenance costs for operators, ensure faster optimization cycle resulting in higher customer satisfaction, and help to reduce the carbon emission to protect the environment. According to 3GPP specifications, a logged measurement configuration message is utilized for configuring a UE to perform the MDT functionalities. However, it is not clear how to extend the MDT functionalities to support MBMS MDT function.